10．has seen　[考查时态和主谓一致。根据时间状语In recent years可知，本处应用现在完成时，主语the Saturday before Christmas为单数，故用has seen。]

　　Ⅰ.阅读理解

　　A

　　NASA has recently found a twin Earth in the Milky Way. Scientists said the planet was the closest to Earth that has been seen.

　　Kepler 452b, which has been named Earth 2, is six billion years old. It has a 385-day year and orbits its star at the same distance as us. It is so like Earth that NASA believes it is possible that life once inhabited the planet. Kepler 452b is 60 percent larger in diameter (直径) than Earth. Scientists say that the planet received the same kind of sunshine as we do on Earth. Thus, plants could survive if taken to the planet.

　　Since the planet is 1.5 billion years older than Earth, scientists say it can show a possible future for earth. “If Kepler 452b is indeed a rocky planets, its location could mean that it is just entering an uncontrollable greenhouse period of its climate history.” Said Doug Caldwell, a scientist working on the Kepler Mission.

　　According to Caldwell, the increasing energy from its aging sun might be heating the surface and evaporating any oceans. Kepler 452b could be experiencing now what Earth will undergo more than a billion years from now, as the Sun ages and grows brighter.

　　The discovery also gives new hope that alien(外星人) civilizations may exist beyond the Solar System. “We won’t be going to this planet but our children’s children’s children might be.” said Jeff Coughlin, another research scientist on the Kepler Mission.

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